Magnetic speedometer



Feb. 19, 1929.

F. F. DORSEY MAGNETIC SPEEDOMETER Filed Sept. 28. 1926 Patented F eb. 19, 1929.

Unirea STATES PATENT OFFICE.

I `FARNUM F. DO RSEY, OF ROCHESTER, NEVI YORK, ASSIGNOE TO NORTH EAST ELECTBIC COMPANY, OF ROCHESTER, NEW' YORK, A CORPORATION OF NEW YORK.

MAGNETIC SPEEDOMETER.

Application filed September This invention relates to speed measuring instrunents of the magnetc type, in which a revolving magnetic field is caused to rotate a spring-controlled indicator by neans of the inductive eflect of the field.

In instrumente of the type in question, as used on motor vehicles, it is usual to drive the revolving magnet or other part by means v of a fieXible sha-.ft connected with the mechanisin of the vehicle, and owing to the position of the instrument upon the uprght or shghtly inclined instrument board, it is most con-` provide a speeclometer in which the foregoing i requirements are fulfilled, but without the necessity of using gears or fleXible driving connections to permit the parts to' have the,

position above described. I have discovered that this may be acconplished by revolving the magnet up on an aXis inclined at a substantial angle 'to the pivotal aXis upon which the indicator is mounted. While this results, in a nagnetic field which revolves in a plane which is not normal to the pivotal aXis of the indicator, the parts may be so proportioned and relatively located that this field produces a sufficiently steady and powerful torque upon the indicator to produce the required 1novement. i i

In instruments of the type in question, it has been customary to use an indicator consistingof thin sheet aluninun or other conductivo material of light weight, and to pro vide this indi cator with an integral'supporting arin which isfixed, at its inner end, to the pivot-stati by which ,the indicator is rotatively supported. In this Construction difliculty hasbeen encountered in providing a supporting arm of. sufiicient rigidity, and a second object of the present invention is to improve the Construction of the instrument with respect to the manner in which pivotal support is provided for the indicator. To this end, I attach the pivot-stafi" toa station- 28, 1926. Serial No. 138,?)14.

indicator and may be formed of material harder and more rigid than that which, for

'electrical reasons, is used inthe indicatoritself.

In the accompanying drawings, Fig. l is a plan-view of the interior 'parts of a speedome'ter embodying the present invention. Fig. 2 is a side elevation, partly in section, of the instrument of Fig. 1, together with the casing within which it is enclosed; and F ig. 3 is a partial sectional view of a modified form of Construction.

The invention is illustrated, in Figs. 1 and 2, as embodied in a speedometer having an indicator 5 in form of a generally cylindrical shell drawn from thin sheet metal such as aluminum. In these two figures the parts are shown as about twice the actual size. The in i dicator is surrounded by a stationary magnetic mass or inductor 6, formed from sheet steel drawn to generally cylindrical form. The indicator is arranged to turn about a vertical axis. i

The magnet 7, by which the revolving field is produced, has the usual form of a divided ring, and it is fixed on the upper end of a drive-shaft 8. The inductor 6 is provided with a window 9 at the front, through which graduations on the o'uter surface of the indicator will be visible. The sh aft 8 is journallod in a frame 10 having, at the bottom, a threaded projection 11 which extends outwardly through an opening in the casing 12 of the instrument. The flexible sha'ft by which the driVe-shaft 8 is actuated may be enclosed ina flexible housing attached to the projection 11 in the usual manner. The usual odometer 13 may also be enclosed in the casing 12 and driven from the shaft 8 by suitableconnections, such' as a worm shaft 14-. The magnet 7 is shown as mounted upon a shell 15, of brass or other non-magentic material, fixed to the upper 'end of the driVe-shaft 8. i

As shown inFigs. 1 and 2, the drive-shaft is inclined at an angle of 309 from the vertic-al, While the indicator is pivoted to turn `upon a vertical axis. The magnetthus produoes a rotary field ina plane inclined at 30 to the horizontal This field, particularly' near the ends of the magnet, passes through the cylindrical body of the indicator from one ductive sheet-1netal draWn into cup-like form at its middle portion, of ,two piVot-bearngs atranged coaxially With the indicate? and located at a substantial distance apairt, .With one hearing fixed to the indicator near the bottom of the cup-like part thereof, a rigid yoke-menber interconneeting the tWo bearings, 21 pivot-staff seated, at its ends in said bcarings, and a 'igd stationary arin attached to and supporting the pivot-stafi.

4. In a magnetic speedonete', the combination, With an indicator consisting of conductive sheet-metal, of 21 yoke-menber pro Vided With a pivot-hearing at one end and a screW-threaded opening at the other end, a screw engaging said opening and securing the yokc-menher to the middle of the indicato', said screw being provided With a pivot-hearing, a pivot-stafl engaging said bearings at its ends, and a stationary member having a rigid arin to the end of which the pivot-stafi" is fixed.

5. In a niagnetic speedoneter, the combinzttion, Withan indicetor, of conductive sheet metal, having the form of a concaVo-convex surface of revolution and pivotally mounted upon its aXis of symmetry, of a shalt journalled on an aXis intersecting, at a substantial angle, said axis of synmetry, and a na net, mounted on and revoluble by said shaft, in a position such that its poles describe a circle adjacent the concave surface of the indicator, which circle is approximately concentric With the pe'mete' of the sectionof the i'ndiczttor in the plane of said circle.

FARNUM F. DORSEY. 

